Electric-circuit-controlling device



Feb. 12; "1929. v1,701,757

` J. M. LEAl ELECTRIC CIRCUIT GONTROLLING DEVICE l Filed April 15, 1922 5mm/nto@ off/W Patented Feb. 12, 1929.

' UNITED STATES JOHN I. LEA, F DETROIT, MICHIGAN.

ELEGTRIC-GIRCUIT-CONTROLLING DEVICE.

Application led April 13,1922. Serial No. 552,396.

The invention relates to devices for controlling and protecting electric circuits and more particularly for preventing injury to parts and excessive loss of current 1n electric systems upon the occurrence of short circuits therein. While in some respects not limited to such use, it is of especial utility in connection with electric systems such as are employed in motor vehicles and which include a storage battery for the supplying of current to electric starting, lighting and ignition devices. U

The principal object of the invention is to provide new and improved means adapted to be heated Vby electrical energy and operative upon excessive ilow oty current to interruptV the circuit in which such flow occurs. In one embodiment of the invention such interruption may be accompanied by the insertion in series in the protected circuit of a heating coil which maintains the circuit breaker in position to prevent further heavy discharge until the short circuit is remedied, thus reducing to a minimum the total loss of energy. In another embodiment' the interruption may be complete but only temporary, recurring immediately, however, as soon as the circuit is again closed should the short circuit still remain in effect. Means may also be provided whereby, upon the operation of the circuit breaker, a signal will be actuated to indicate the occurrence of a short circuit or of an abnormally hi h rate of current iow. Such signal is pre erably arranged to be actuated intermittently and means may be provided to prevent injury to the thermally actuated circuit breaker should the signal circuit also contain a short circuit.

The circuit interrupting devices are preferably so constructed and arranged as to permit of their insertion in placev ci? fuses or like protective devices in circuits Where the latter are generally employedand are particularly suitable for circuits operating" under relatively low voltage and of non-inductive character such, for example, as those of motor vehicle lighting and ignition systems. For this purpose the circuit interrupting means is preferably embodied in a self contained unit of such form and size that it may be mounted between fuse clips of conventional character, the fuses being rendered unneces# sary by the use of the improved device, or may be otherwise removably mounted in place of analogous protective mechanisms.

Further objects and advantages will appear from the following description taken in connection with the accompanying drawings in which Fig. 1 is a plan view of one form of device in which the invention may be embodied,

Fig. 2 is a longitudinal section online 2--2 of Fig. .1, t

Fig. 3 is a transverse section on line 3--3 of Fig. 2,

- Fig. 4 is a plan view of another embodiment of the invention,

Fig. 5 is a section on line 5--5 of Fig. 4,

Fig. 6 is an end elevation of the structure shown in Fig. 4 looking from the right of Fig. 4, j

Fig. 7 is a wiring diagram illustrating the application of the device shownv in Figs. 1,

Fig. 8 is a wiring diagramy illustrating the application of the device shown in Figs. 4,

5, 6, and

,F ig. 9 is a wiring diagram illustrating a slight modification. l

Referring iirst to the structure shown in i Figs. 1 to 3, 11 indicates a plate of suitable conducting material such as brass, which plate is bent upwardly adjacent to one end to form wings 12, 13, adapted to iit between and be firmly ,held by the-arms of a spring clip 14. A second conducting plate 15 secured to the plate 11 at one end is formed at the other end with Wings 16, 17, similar to the wings 12,13, and adapted to fit between the arms of a second spring clip 18. The clips 14, 18, are of a type commonly employed for the mounting o fuses, which latter may bereplaced `by the device illustrated, and will be suitably connected in series with the circuit to be protected.

The adjoining ends of the plates 11 and 15 are superposed and secured together in any convenient manner as by lugs or anges 1,9 on the plate 11 which areloent over the plate 15 as shown. A sheet of insulating material 2O is interposed between the plates and preferably coversthe entire inner surface of the plate 11. A blade 21 of bimetallic thermostat material is clamped upon the end of the plate 15 and in conducting relation thereto as by the lugs 19, the insulating material 20 preventing contact of the blade with the said lugs. The blade is properly ositioned by providing holes 22 therein w ich t over slight projections 23 struck up from the 11 vio plate 15. The free end of the blade extends `over the plate 11 and carries at its extremity a contact 24 so positioned as to engage normally with a contact 25 mounted upon the plate 11. A heating coil 26, which may be of nichrome or similar material, is arranged in heating relation to the blade 2l as by being wound thereon and insulated therefrom and is connected at one end to the blade and at the other end to the plate 11.

The operation of the device already described may be understood by reference to Fig. 7 in which the thermostatic circuit breaker is shown diagrammatically in connection with a circuit including a battery B and one or more translating devices such `as lights 29 control of which .may be had by means of a switch S. The arrangement is such that the current utilized by the translating deviceswill flow normally through the blade 21 and the contacts 24, 25. Assuming, however, that a short circuit should occur between the protecting device and the translating devices, as, for example, at the point 30, then the flow of current through the blade upon the closing of the switch S will be greatly in excess of the normal flow. As soon as .such flow exceeds that for which the blade is calculated and adjusted the heating effect causes the blade to be defiected and the circuit to be interrupted at the contacts 24, 25, the blade being so mounted that it tends to move away from the contact 25 as the temperature rises.

In the absence of some provision for the maintenance of an elevated temperature affecting the blade 21 the interruption of the circuit will be only temporary, since, as soon as the blade cools sufficiently, the contact-s will again engage. Even without such provision the loss of current will be substantially negligible inasmuch as the heating effect due to excessive current' is such as to cause almost instantaneous deflection of the blade. In fact it has been found that continuous operation of the device for several hours does not appreciably lower the battery charge as indicated by hydrometer tests. Means may be provided, however, for maintaining the interruption in effectso long as the abnormal conditions exist as, for example, by the use of the coil 26. The arrangement is such that when the contacts 24, 25, are disengaged by the movement of the blade 21 the heating coil is inserted in series in ,the protected circuit. The current which then flows through the coil, which is of relatively small value, because of the high resistance of the coil, produces a heating effect the extent of which may be predetermined by selection of the characteristics of the coil. f

The coil may operate, therefore, either to heat the blade to such an extent that after the contacts have .once separated the blade will remain in deflected position so long as the short circuit remains in effect, or it may. ermit initially a few reciprocations of the b ade before the heating efiect becomes sufficient toA maintain the deflection of the blade. Should the heating effect be still less it may operate merely to delay the cooling of the blade so as to render less rapid the return movement to circuit-closing position.

Whether the heating coil is utilized or not, I preferto arrange some form of signal `device in such relation to the system that the abnormal conditions resulting in excessive current discharge may be brought to the attention of the operator. For this purpose the ammeter A maybe employed as illus# trated, being located between the source of4 current and the protective device. Very abrupt oscillations of the indicator to its extreme limits of movement will accompany the momentary discharges of current through the protective device and thus advise the oper` ator of the occurrence and nature of the de' rangement in the system. t

Referrin to the form of the invention 1l1ustra-ted in Flgs. 4,5 and 6, 31 indicates a base plate which may be provided with upwardly extendin fianges 32, 33, 34, to partially enclose an protect the thermostatic devices mounted upon the plate. An ear 35 extends laterally from the base plate which may serve as a means of attachment of the device to a supporting structure and also to connect the plate to a conductor in the circuit to be protected. A contact plate 36 and two end connector plates 37, 38, suitably insulated from each other and from the base plate 31, are fastened together and to the'base plate in any convenient manner, as by rivet 39. Binding screws 40, 41, may be provided to connect the plates 37, 38, respectively to a signal circuit and to the main circuit to be protected. Two contact members 42, 43, of bimetallic thermostat material are secured in position lby the rivet 39, the member or blade 42 being in conducting relation to-the connector plate 38 and the blade 43 in similar relation to the plate-37, and both blades being so arranged as to move upwardly when heated, or away from the positions represented in the drawing. A series of contacts 44, 45, 46, and 47 are mounted respectively on the base plate 31 and the free extremities of the members 42, 36 and 43. These contacts are superposed substantially in alignment so that each contact is in position to engage the next adjacent contact either above or below. The parts are normally so positioned that the contacts 44 and 45 will be in engagement and likewise the contacts 46 and 47 The terminal plate 38 is therefore normally in conducting relation with the base plate 31 through blade 42 and contacts 44, 45, while the terminal plate 37 is in conducting relation to the intermediate plate 36 through blade 43 and contacts 46, 47. A heating coil 48 may be arranged in heating relation to the blades 42 and 43 as by being mounted upon but `insulated from the parts 36, 42, the ends of the coil .being connected respectively to the blade 42 and the base plate 31.` The device as illustrated is especially' designed to replace the vibrator employed in certain types of motor vehicle lighting and ignition switches.

The operation of this form of the invention will be understood by reference to Fig. 8, wherein the device is illustrated as applied to a motor vehicle electric system including a battery B,translating devices such as the lamp 49, and a signal device, shown in this instance as a horn 50 which may be the horn ordinarily employed by the driver as a warning signal. The blade 42 is connected in series in the main circuit so that current normally flows to the translating devices through the blade 42 and contacts 45`r 44. The blade 43 is connected to the horn. Should the main circuit become grounded at some point between the protect-4 ing device and the translating devices, as indicated at 51, a heavy discharge will take place through the blade 42 thus heating it and 'causing the immediate separation of the conmediate plate 36 whereby it completes a circuit through blade 42, contacts 45, 46, 47, and blade 43 to the horn 50. Disregarding the et feet of the coil 48, which may be omitted if desired, the horn will continue to sound for a few seconds or until the cooling of the blade 42 causes the separation ot the contacts 45, 46. When the blade cools suliiciently to permit the re-engagement of the contacts 44, 45, a momentary heavy discharge will take place through the blade 42 followed by a repetition of the warning signal. Supposing, however, that the signal circuit should become grounded between the protecting device and the horn, as indicated at 52, then the blade 42,

when it acted to complete the alarm circuit,

would still be subject to heavy discharge of current by reason of the short circuit at 52. lUnless some means were provided to prevent it such heavy discharge would quickly fuse the blade and, while this would serve to completely interrupt the circuit, as with an ordinary fuse, it would necessitate the replacement of the device in order to re-establish the working circuit. This inconvenience may be avoided by the use of the blade 43. Should a heavy discharge take place through this blade it will cause separation of the contacts 46, 47, thereby interrupting the signal circuit until the blade again cools. The only effect of a short circuit in both the main and signal circuits.there tore, it will to cause a more or less rapid alternation in the making and breaking of the circuits through the two thermostat blades. The total loss of current through such operation is substantially negligible, whereas the magnetic vibrator which the device is designed to replace usually consumes about eight and one half amperes when in operation.

The operation as above described may be modified by the effect ot the heating coil 48. This coil, upon the separation of contacts 44, 45, will act, as in the form first described, to retard the rate of cooling of the thermostats and thereby delay the repetition of the cycles of operation. It may even operate after a certain time interval has elapsed to prevent entirely the return of the thermostats to their original position while the short circuit reH mains in eli'ect, thus acting, after the signal has been operated for a time, to maintain the circuits open with only the expenditure of the current required for the heating coil, which amount may be exceedingly small.

In Fig. 9 is illustrated diagrammatically a form of the invention similar to that shown in Figs. 1 to 3 but combined with a signal (ii-cuit including a horn 50. A back contact 54 is interposed in the signal circuit. Upon the occurrence of a short circuit as indicated at 30, the. deflection ot the blade 21', similar to the blade 21 of Fig. l,.will result in the closing of a circuit through the horn by Way of a fixed contact member 54. The signal will therefore be sounded intermittently so long as the conditions continue which would otherwise permit a heavy discharge of current. in the main circuit. No provision is made. in this case for protection in the event of accidental grounding of the signal circuit. This torni of the invention differs therefore from that shown in Figs. 4. 5, 6 and 8 in the omission ot the thermostatic circuit breaker 43` while it adds to the form shown in Figs. 1, 2, 3 and 7 the provision of a back contact operating a signal circuit.

The thermostat blades employed may be ot the well-known type comprising a plate o't brass and another ot iron which is one halt the thickness ot the brass or less, the two being so secured together that differential expansion of the two plates will cause deflection of the blade. For use in carrying out the present invention the dimensions of the blade and its conducting capacity must be so detcr- .mined that it will carry all ot the normal working current wit-hout being heated tliereby to such an extent to cause separation of the contacts. On the other hand. in order to prevent waste of current and injury to other devices in thepcircuit upon the occurrence of a short circuit, the thermostat should be sutliciently sensitive to be deflected substantially instantaneously under the influence of excessive discharge. Furthermore. it the blade is designed for quick response to heavy ow ot current it would be readily fused should such flow continue for an appreciable time 'and this also necessitates quick interruption of the circuit it the blade is to be preserved.

Bimetallic blades of the type mentioned are los lli?

CAD

peculiarly adapted to perform the required function because, after the predetermined critical current How has been exceeded, the temperature rises very rapidly, due, possibly, not only to increased resistance accompanying the rise in temperature but also to the dit'- t'erent conductivities of the two metals as a result of which the greater part of the discharge takes place through the brass and thereby disproportionately increases the temperature of the latter and its rate of expansion. Tests made with a blade so proportioned that it would carry approximately 14 amps. without breaking the circuit have shown that a discharge resulting. from the short circuiting of an ordinary automobile starting and lighting battery through the blade will produce what may be properly termed a snap action causing the blade not only to interrupt the main circuit very abruptly but to continue its movement after the circuit is actually broken and thereby engage the contact in the signal circuit and relmain in engagement therewith for an appreciable time.

It will be understood that a signal may be given upon the occurrence'of a short circuit vtion may be made without departing from thefspirit and scope of the invention and therefore I do not wish to be limited to the features as described except as required by the language of the claims in view of the prior art.

I claim:

l. An electric circuit controlling device comprising a conducting base member, a second conducting member mounted upon said base member and insulated therefrom, and a thermostat blade secured at one end in conducting relation to said second member and having its free endnormally in conducting relation to said base member, and a heating coil mounted in heating relation to said thermostat and arranged to be traversed by current upon the separation of said contacts.

2. An electric circuit controlling device comprising a conducting member adapted to be connected in an electric circuit, a second conducting member secured to the first but insulated therefrom and adapted to be connected in said circuit, a thermostatic blade secured in conducting relation to one of said members and insulated from the other, cooperating contacts on said other member and the free end of said blade and a heating coil Wound upon said blade and having its ends connected respectively to said conducting members.

3. In means for protecting an electric circuit, the combination with a conductor ot said circuit of a' conducting element in series therewith, heat-responsive means adapted to circuit, a thermostatic elementarranged to cause separation of said contact members upon the occurrence of abnormal flow in said circuit,'and a heating coil arranged in shunt with said members and in heating relation to said element, the connections being so arranged that heating current continues to flow in said coil after separation of said contact members.

5. In means for protecting an electric cir` cuit, the combination with a conductor of said circuit of a circuit-interrupting device therefor constructed and arranged to move normally towards circuit-closing position, heatresponsive means adapted to cause movement of said device to interrupt said circuit upon the occurrence of excessive iiow therein, and means-tending to oppose return of said device to circuit-closing position during the continuance of the abnormal condition tending to cause such excessive iiow.

6. The combination with an electric circuit of mechanism orpreventing continued excessive current iiow therein comprising a pair of contacts in said circuit, a current conducting thermostat in said circuit arranged to cause separation of said contacts by movement of the thermostat due to temperature increase, vsaid thermostat being so proportioned relative to the maximum excessive current whose continuance is to be prevented that it will be given substantially a snap action by passage therethrough of the said current, a second pair of contacts arranged to be closed by movement of said thermostat after separation of the first pair and means for causing intermittent interruption of current flow through said second pair of contacts so long as they tend to be held closed by the action of said thermostat.

In testimony whereof I afx my signature.

JOHN M. LEA. 

